Information processing apparatuses employ, as their storage apparatus, chiefly semiconductor memory and magnetic memory. The semiconductor memory is used as an internal storage apparatus because of its short access time, and the magnetic memory is used as an external storage apparatus because of its large storage capacity and non-volatility. Two major types of magnetic storage, a magnetic disk and a magnetic tape, are today in widespread use, in which a magnetic thin film formed on an aluminum disk or resin tape is used as a recording medium. To record magnetic information onto the recording medium, a functional component performing electromagnetic conversion operation is used. To reproduced the magnetic information once recorded, another functional component performing magnetoresistive or giant mnagnetoresistive phenomenon or electro-magnetic induction phenomenon is used. These functional components are arranged in an input/output unit called a magnetic head.
The magnetic head moves relative to the recording medium, to record magnetic information at any particular location on the recording medium and to reproduce, as required, the magnetic information recorded. A magnetic disk unit is now discussed for illustration purpose. As shown in FIG. 2, a magnetic head is made up of a recording component 21 for recording magnetic information and a reproducing component 22 for reproducing magnetic information. The recording component 21 is made up of a coil 26 and magnetic poles 27, 28 which wrap the coil 26 at its top and bottom and which are magnetically coupled. The reproducing component 22 is made up of a magnetoresistive effect pickup 23 and a conductor 29 for conducting a constant current to the pickup 23 and for detecting a resistance change. Disposed underneath the reproducing component 22 is a magnetic shield layer 25 which prevents intrusion of unwanted magnetic flux. The pole 28 has the same magnetic shielding effect. The narrower the so-called read gap, namely the clearance between the magnetic pole 28 and the shield layer 25, the less unwanted magnetic flux intrudes into the magnetoresistance effect pickup 23, the better discrimination results and therefore the more high-density magnetic information is handled. These functional components 21, 22 are formed on a primary layer 24 on top of a magnetic head body 30.
The performance of a magnetic storage apparatus is determined by the speed of input/output operation and its storage capacity, and to enhance the performance of the magnetic storage apparatus, a short access time and a large storage capacity should be achieved. There is today a growing demand for a compact magnetic storage apparatus from the standpoint of space saving and ease of use. To meet such a demand, a magnetic storage apparatus capable of recording and reproducing a great deal of magnetic information to and from a sheet of recording medium should be developed. A known example is disclosed in The Journal of The Magnetics Society of Japan, Issue 18, No. 51, page 345. FIG. 18 shows its structure. A magnetoresistive effect pickup 23, interposed between shield films 42, 25, has an electrical contact point with the shield film 42. Thus, the shield film 42 is also used as a conductor. The above disclosure is the prior art in that the direction of current to the magnetoresistive effect pickup 23 is perpendicular to the sliding surface. A conductor 47 is used to control the direction of magnetization of the magnetoresistive effect pickup 23 when a current flows. In the present invention, the conductor 47 is also required, and is disposed between the write magnetic poles. In FIG. 18, however, contact between the magnetoresistive effect pickup 23 and the shield film 42 is performed by an area contact, where magnetoresistive effect is degraded by magnetostriction that takes place in the magnetic thin film because of machining deformation residing after formation of the magnetic poles. It was also learned that Cu as a material for electrodes diffusing through an NiFe layer degraded its magnetic characteristic. In the contact point that is subject to such a problem, intended magnetoresistive effect fails to work satisfactorily and high-sensitivity pickup required for high-density recording cannot be achieved.
To attain a high-density recording, the size of magnetic domains should be miniaturized. Generally speaking, this objective may be attained by narrowing the width w of the recording pole 27 shown in FIG. 2 and by heightening the frequency of the recording current flowing into the coil 26 (frequency against the rotation of the recording medium). Since the signal strength during reproduction depends on the size of the magnetic domains, a miniaturized magnetic domain lowers the resulting signal strength, presenting difficulty in the reproduction of information. Thus, a provision should be made to enhance pickup sensitivity of the reproducing component. However, improvements attainable in this approach are subject to a limitation of physical restriction of magnetoresistance effect presented by a magnetic thin film used in pickup. The limitation of the recording density now widely accepted is a few Gb/in.sup.2.
To overcome this limitation, for example, U.S. Pat. No. 5,041,932 has proposed an integrated magnetic read-write head/flexure/conductor structure where a magnetic head and a recording medium are put into contact. In the conventional magnetic disk device, its magnetic head is airborne on the recording medium, and a layer of air is interposed between the magnetic head and the recording medium. In contrast, the disclosure of the above U.S. Patent employs a magnetic head functional component 43, as shown in FIG. 3, that is embedded into a light-weight, miniature flexure 45, and the magnetic head functional component 43 is slid while being kept in contact with the recording medium 11. Since in the above disclosure, non-magnetic layer is interposed between the surface of the recording medium and the magnetic head functional component (magnetic poles) 43, magnetic information in the recording medium is efficiently transmitted to the magnetic head functional component, and a strong reproduction signal thus results. A magnetic domain, even when miniaturized, offers a high signal to noise (S/N) ratio, and an excellent reproduction signal results.
Since in the above arrangement, however, the magnetic head functional component is supported by a flexible flexure, the deformation of the flexure causes a phase delay or unexpected vibrations when a rotary actuator performs the positioning of the magnetic head.
This problem may be alleviated by a magnetic head 2 that lifts a front pad, as shown in FIG. 4 (Japanese Patent Unexamined Publication No. 6-60329). In this arrangement, the front pad flies or floats high by means of air pressure, and only a rear pad having a device functional component 46 remains in contact with a recording medium 1. With the front pad floated, the load acting on one rear pad is reduced to the load of the magnetic head minus flying force. Reducing the load acting on the rear pad permits the load acting on the entire magnetic head to increase accordingly. If a larger load is permitted on the entire magnetic head, rigidity of suspension members and the like for supporting the magnetic head will be increased. Thus, a reliable input/output operation is assured compared to the mechanism of the magnetic head supported by the flexure.
However, the magnetic head must be kept light. For example, Japanese Patent Unexamined Publication No. 5-114116 requires the entire magnetic head to be 1.5 mg or lighter.
As described above, the usual technique allows magnetic information to be recorded and then reproduced in a high density with the magnetic head keeping contact sliding with the recording medium. However, it is learned that a further attempt to increase the recording density presents the following problem.
Since the front pad is afloat, the front side of the magnetic head floats greatly as the recording medium rotates at its high circumferential speed region, and as shown in FIG. 4, the clearance a between the poles constituting the device 46 and the surface of the recording medium 1 is made larger. This broadens a recording magnetic field distribution, a resulting spacing loss degrades electromagnetic conversion efficiency in reproduction, and intended high-density information cannot be input nor output.
To keep the magnetic head in the position shown in FIG. 4, the front pad size should be large. When the recording medium comes to a halt, the front pad of the magnetic head that was afloat is put down into contact with the surface of the recording medium. If the front pad size is large, the front pad is subject to stick because of a lubricant existing between the pads and the recording medium. Stick results from cohesive force, adhesive force, and surface tension of the lubricant filled between the pads and the recording medium, and is so strong that simply rotating of the recording medium may not separate again the pads from the recording medium. Any attempt to forcibly rotate the recording medium with the pads stuck thereon may cause damage such as a damaged suspension system of the magnetic head or a peeled magnetic thin film that forms the recording medium.
To prevent stick, Japanese Patent Unexamined Publication No. 6-44718 discloses a magnetic head that has, on its sliding surface, a strut having a small contact area. Disadvantages with this disclosed arrangement are that the manufacturing steps of the strut is more complex than those of ordinary components, and that the strut contacts the medium during low floating (contact sliding) operation.
U.S. Pat. No. 5,424,888 discloses another arrangement, in which stick is prevented by tapering the front pad and the rear pad of a magnetic head. Since the purpose of this arrangement is to help float of the magnetic head while preventing stick, the tapered pad is never put into contact with the recording medium during recording and reproduction. To test the adaptability of this magnetic head to a high-density recording medium, a recording and reproduction test was performed with the pad kept in contact with the recording medium. Test result was to provide a poor reproduction signal. This is because the pad area in contact with the recording medium is large enough to give a large tangential force (frictional force) and to force the magnetic head to vibrate.
Further, to keep the magnetic head in the position shown in FIG. 4, the flying force of the front pad should be balanced with rigidity of the gimbal member of the suspension system for supporting the magnetic head. Beside keeping the magnetic head in its position, the gimbal member absorbs machining tolerances and assembly tolerances of the magnetic head, the suspension system and arm members taking place when they are machined and assembled, so that the surface of the pad on which the device is mounted is put into contact with the surface of the recording medium.
In a magnetic storage apparatus that allows its magnetic head to be in contact with its recording medium, the magnetic head should be lightly weighted to lessen abrasion of the magnetic head and recording medium and to prolong the life of the apparatus. To mate the pad surface with the surface of the recording medium under such a light load condition, the suspension system should have an extremely low-rigidity gimbal. Suspension systems now available at an inexpensive price are made typically of stainless steel. We the inventors have learned that an intended rigidity is difficult to achieve, considering that wiring for a device should be installed on the gimbal section of the suspension system and that the gimbal needs manufacturing through metal stamping process that is suitable for quantity production.
Further, the shape of a magnetic head sliding surface is described in Japanese Patent Unexamined Publication Nos. 6-60329 and 6-150283, for example. These heads disclosed assured a stable and continuous contact sliding within a limited range of yawing angle. The following problem, however, arose when a contact sliding test was performed within the yawing angle specified in our invention. FIG. 14 shows the test result of each prior art head in connection with the relationship between the yawing angle and the output of the magnetic head. FIG. 14a shows the test result obtained from the magnetic head made up of the pads 51-a, 52-a, and 53-a according to Japanese Patent Unexamined Publication Nos. 6-60329 and 6-150283, and FIG. 14b shows the test result obtained from the magnetic head made up of the pads 51-b, 52-b, and 53b according to Japanese Patent Unexamined Publication No. 6-150283. A high output level (namely, a good output) was obtained only within a yawing angle of .+-.10.degree. in FIG. 14a or within a yawing angle of .+-.15.degree. in FIG. 14b. These disclosed examples thus failed to satisfy the performance requirement our invention meets in achieving a reliable input/output operation over a wide range of yawing angle. After studying the examples, we learned that the magnetic head when the yawing angle was set to .+-.15.degree. or more. The above disclosures did not address this problem, and this embodiment is the first one that focuses on this problem. To attain a large storage capacity in a magnetic storage apparatus, the surface of the recording medium should be effectively utilized. This objective cannot be achieved by these disclosed prior techniques only.
Japanese Patent Unexamined Publication No. 6-60329 discloses a three-pad type magnetic head with its front pads floated. In this case, however, the front pads float high by air pressure (as high as 50 nm), and if the circumferential speed varies greatly, the flying force varies as well, making unstable the contact sliding operation (thus, input/output operation). The problem encountered herein agrees with the problem presented in FIGS. 14a and 14b. In the shape of the pads in our invention, excess lubricant is reliably rejected without floating or flying the front pads 51, 52. Therefore, a reliable input/output operation was achieved within a wide range of yawing angle. PA1 Other examples that employ a sharpened pad on a sliding surface are disclosed in Japanese Patent Unexamined Publication Nos. 4-281209, 1-298585, 6-52645, and 2-101688. Since these are of a flying head, the pad should generate flying force. For this purpose, the pad area should be large, and the same pad obviously fails to serve the purpose of the present invention where the head remains in contact with the medium. According to the test, the pad area should be less than 2.5.times.10.sup.-8 m.sup.2 to prevent the pad from flying. To embody the present invention, therefore, the pad size should be restricted. PA1 In the pad disclosed in U.S. Pat. No. 5,424,888 having its taper on its entire surface, the pad surface comes close to the surface of the recording medium as shown in FIG. 24a. Since a pad surface 83 formed on the pad 53 is a flat plane, a sharp edge comes close to surface of the recording medium. The magnetic head was put into contact sliding in such a position relative to the recording medium, the sharp edge portion was rapidly abraded. When abrasion advanced, a new surface was formed generating a flying force larger than originally calculated in design stage. This made it impossible to keep the contact engagement between the magnetic head and the recording medium at the value originally intended at design stage. Furthermore, abrasion induced a great deal of powder, leading to a serious crash problem.
For the above reasons, the pad area for floating the magnetic head cannot be made small, the problem of stick cannot be solved, and thus the magnetic storage apparatus having a floating front pad is subject to a limitation in an effort of high-density recording design.
It is an object of the present invention to provide a novel magnetic head that constantly allows itself to be in contact with a recording medium and to provide a magnetic storage apparatus of low-price, large storage capacity and high recording density employing the magnetic head.